This proposal is a continuation of last 14 years' studies aimed at further elucidation of the mechanism of renal and intestinal transport of amino acids, sugars and electrolytes. Research work performed in this laboratory in the last 14 years have shown that there is a structural specificity in renal tubular transport of aromatic amino acid and sugars. Using the microperfusion and micropuncture techniques we have shown a bidirectional transport system for sugars and aromatic amino acids. We plan to use the combination of microperfusion into a surface loop of proximal tubule and the microinfusion into a peritubular capillary of rat kidney to study the transport processes of such aromatic amino acids and the interactions. The major objectives are to determine: (1) the structural requirement for the renal transport of such amino acid derivatives; (2) the effect of heavy metals, especially lead and mercury, and some metabolic inhibitors on the renal transport of the amino acid derivatives. Studies with fetal and fish intestinal preparations in this laboratory have also shown that fetal intestine lacks a structural specificity for amino acid transport seen in the adult, and that fish intestine exhibits a simultaneous active transport of sodium and chloride ions. It is our plan to continue our studies by using the Ussing chamber technique to study; (3) the mechanism of chloride transport across fish intestine and whether or not chloride transport also occurs in fetal intestine; (4) the effect of bacterial enterotoxin, especially cholera, staphyloccal and pseudomonas toxins, and vasopressin on ion transport and permeability of intestine.